Method of generating an x-ray beam composed of a plurality of wavelengths



Dec. 24, 1968 N, sPlELBERG ET AL v 3,418,467

METHQD OF GENERATING AN X-RAY BEAM CONFUSED OF A PLURALITY OF WAVELENGTHS Filed Feb. 17, 1965 SYNTHES/ZE'D sPxmz/M INVENTORS. NATHAN sP/aams BY JOSHLM LADf'LL United States Patent 3,418,467 METHOD OF GENERATING AN X-RAY BEAM COMPOSED OF A PLURALITY 0F WAVELENGTHS Nathan Spielberg, Hartsdale, and Joshua Ladell, Monsey, N.Y., assignors to North American Philips Company,

Inc.

Filed Feb. 17, 1965, Ser. No. 433,282 7 Claims. (Cl. 25051.5)

ABSTRACT OF THE DISCLOSURE Our invention relates to a method of producing a beam of penetrating radiation of predetermined spectral distribution and intensity. In particular, this invention relates to the synthesis of a polychromatic X-ray beam in which several wave lengths of X-rays, each of predetermined intensity, are combined.

As is Well known, an X-ray tube emits a continuum of radiation known as the Bremstrahlung on which may be superimposed characteristic radiation of the target, it the potential applied to the target is suflicient to generate the characteristic radiation. Thus, any X-ray tube emits a polychromatic beam of X-ray radiation which includes all wave lengths up to the shortest wave length determined by the target voltage.

With the use of filters, monochrom-ators, and the like, a particular wave length, usually the characteristic wave length of the target may be selected for further utilization.

For certain applications, it may be desired to have a polychromatic beam of X-radiation in which several selected wave lengths are present in suflicient intensity so that they may be effectively utilized. Ordinarily, this is not feasible since the Bremstrahlung has a greatly reduced intensity as compared to the characteristic radiation from the target so that selected wave lengths therefrom would have such low intensity that they could serve no useful purpose.

It is a principal object of our invention to provide a method of synthesizing a beam of penetrating radiation in which several wave lengths each of predetermined intensity are present.

Another object of our invention is to provide a method of combining penetrating radiations of diflerent wave lengths from separate sources into a composite beam in which each of the component radiations are present.

A still further object of our invention is to provide a method of producing a beam of penetrating radiation in which are present diflerent wave lengths of radiation each having a predetermined intensity.

A still further object of our invention is to reinforce the intensity of a given wave length in a beam of X-radiation by combining the radiation of said wave length emitted from two or more sources.

These and further objects of the invention will appear as the specification progresses.

In accordance with the invention, we employ a plu- "ice rality of X-ray tubes, or other sources of penetrating radiation such as radioactive preparations, neutron sources, etc., each of which emits a particular wave length of radiation in addition to any continuum of Bremstrahlung which also may be present, as in the case of an X-ray tube. Radiation from each of these sources is intercepted by a special ditfracting crystal which reflects each desired Wave length in the same direction so that a composite beam is formed containing all the component wave lengths emitted by the several sources.

In order to control the intensity of the several component radiations in the resultant beam, the intensity of each component is controlled at the source thereof. In the case of an X-ray tube, this maybe effected by controlling the voltage and current supplied to the tube, or by means of a radiation absorber which can be interposed between the tube and the crystal, whereas in the case of a radioactive or neutron source, absorbers will be placed between the source and the crystal.

The crystal that is employed to reflect the radiations from the several sources must satisfy the same conditions for simultaneous reflection of several wave lengths of radiation to each of several detectors as disclosed in US. Patent 3,046,399.

Briefly, the crystal must satisfy the Lane condition for N characteristic radiations and at least N sets of crystal- 10 graphic planes.

The invention will be described in greater detail with reference to the accompanying drawing in which the sole figure illustrates an arrangement for carrying out the method according to the invention.

Referring to the drawing, X-ray tubes 1, 2, 3, 4 and 5 are positioned so that X-rays emitted by each tube are intercepted by difiracting crystal 6. Each of the tubes 1 to 5 is provided respectively with an anode or target of Cu, Ni, Cr, Sn and Mo respectively. Thus, when these tubes are energized, i.e., by applying a suitable potential to each, each tube will emit characteristic X-rays as well as the Bremstrahlung, or continuum. Thus, X-ray tube 1 will emitt CuKa radiation (1.54 A.); tube 2 will emit NiKa (1.66 A.); tube 3 will emit CrKa (2.29 A.); tube 4 will emit SnKoc (0.49 A.) and tube 5 will emit MoKa (0.71 A.). In addition each of the tubes will emit other line spectra, as well as the Bremstrahlung or continuum, some of the wave lengths of which will be so long as to be absorbed somewhere along the optical path.

In order to insure that the radiation from the tube is incident on the crystal at the proper angle, collimators 7, 8, 9, 10 and 11, each of which comprises a plurality of parallel sheets or foils or tubes whose matreials are relatively impervious to X-rays are placed respectively between each of tubes 1 to 5 and crystal 6.

Crystal 6 is a quartz crystal with its surface parallel to the (104) crystallographic planes. With each of the X-ray tubes then positioned at the intersection of the spheres of reflection (commonly tangent at the origin of the reciprocal lattice of the crystal and with radii proportional to the reciprocal wave lengths of the Km radiations) with a reciprocal lattice point, each of the wave lengths (Ka) emitted by tubes 1 to 5 will be reflected by the crystal and emerge as a composite beam 12. Thus, in accordance with the principles described in US. Patent 3,046,399,

tube 1 will be at reciprocal lattice point (104); tube 2 at reciprocal lattice point (203 tube 3 at reciprocal lattice point (102); tube 4 at reciprocal lattice point (308 and tube 5 at reciprocal lattice point (10?). Consequently beam 12 will contain those wave lengths corresponding to the Kot radiations of tubes 1 to 5, all other wave lengths being reflected in other directions if they are intercepted by the crystal at all.

The intensity of each wave length in beam 12 may be controlled, in this case, by regulating the tube current and voltage for each tube. This may be accomplished, as is well known, by controlling the various operating potentials (anode voltage, heater voltage, etc.) applied to each tube. Consequently, not only is the spectral distribution of beam 12 determined, but the intensity of each wave length in the beam can be controlled.

Crystal 6 if desired may be bent or curved, ground, or curved and ground according to standard focussing techniques to produce a convergent or divergent beam, appearing to emanate from a single source.

It should, of course, be understood, that sources of radioactive radiations, such as radioactive isotopes of the target elements, or neutron sources may be employed instead of X-ray tubes. It may be necessary in such cases, because of the different wave lengths, to employ a different crystal. The principles for preparing and orienting the crystal are the same as those described in U.S. Patent 3,046,399 for the diffracting crystal 3.

Such a beam may be used for non-dispersive X-ray fluorescence analysis where the specimen contains both heavy and light elements which may be selectively excited by one of the wave lengths in the beam thus eliminating the requirement for an analyzing crystal. This beam may also be employed in X-ray radiography and fluoroscopy where images may be obtained simultaneously in the various wave lengths employed and recorded separately in an interleaved stack of photographic plates or registration devices, the interleaving pieces being judiciously chosen absorber foils so that the softer components are recorded in the plates closest to the object being radiographed and the harder components in the plates further away.

Therefore, while the invention has been described with reference to particular embodiments and applications thereof, other modifications will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

What we claim is:

1. A method of generating a beam of penetrating radiation composed of a plurality of wave lengths each having a predetermined intensity comprising the steps of orienting each of a plurality of sources of penetrating radiation each of which emits radiation having at least one Wave length different from that emitted by another source toward a common diffracting crystal, positioning the crystal to intercept and diffract a single wave length of radiation from each of said sources in a common direction, and adjusting the intensity of radiation from each source to thereby form a beam reflected by said crystal containing each of said wave lengths with a predetermined intensity.

2. A method of generating a beam of penetrating radiation composed of a plurality of wave lengths each having a predetermined intensity comprising the steps of placing a diffracting crystal to diffract radiations emitted from a plurality of spatially positioned sources of X-rays each of which emits at least one wave length different from that emitted by another source in a given common direction, said crystal having a plurality of diffracting planes for diffracting in said direction each of a plurality of wave lengths generated in a plurality of sources, pointing each of said sources at the crystal from the direction of a radius drawn from the intersection of a sphere of reflection and a reciprocal lattice point, the radius of said sphere being equal to the reciprocal of said wave length, orienting said crystal to intercept and diffract only said one wave length from each of said sources in said given common direction, and adjusting the intensity of radiation from each of said sources to thereby form a beam of radiation in which each of said wave lengths has a predetermined intensity.

3. A method of generating a beam of penetrating radiation composed of a plurality of wave lengths each having a predetermined intensity comprising the steps of placing a diffracting crystal to intercept and ditfract in a common direction a single wave length of radiation emitted by a plurality of spatially distributed sources of radiation each of which emit radiation having at least one wave length different from that emitted by another of said sources and adjusting the intensity of the radiation emitted by each source to thereby form a beam of radiation diffracted from the crystal in which each wave length has a predetermined intensity.

4. A method of generating a beam of penetrating radiation composed of a plurality of wave lengths each having a predetermined intensity comprising the steps of placing a diffracting crystal to dilfract in a given common direction radiations from a plurality of spatially positioned sources each of which emits at least one wave length different from that emitted by another of said sources, said crystal having a plurality of diffracting planes for diffracting in said direction each of a plurality of different wave lengths generated in a plurality of sources, pointing each of said sources at the crystal from the direction of a radius drawn from the intersection of a sphere of reflecting and a reciprocal lattice point, the radius of said sphere being equal to the reciprocal of said wave length generated in said source, orienting said crystal to intercept and diffract only one wave lengths from each of said sources in said given common direction, and adjusting the intensity of radiation from each of said sources to thereby form a beam of radiation in which each of said wave lengths has a predetermined intensity.

5. A method of generating a beam of penetrating radiation composed of a plurality of wave lengths each having a predetermined intensity comprising positioning a quartz crystal to intercept and diifract in a common direction X-radiation emitted by sources of X-radiation each of which emit at least one of the characteristic wave lengths of Mo, Sn, Cu, Ni and Cr positioned respectively at reciprocal lattice points (101), (308 (405), (205), and (102) of the crystal, and adjusting the intensity of each of said sources to thereby produce a beam of radiation diffracted by said crystal in which the respective wave lengths of each of said sources has a predetermined intensity.

6. A method of generating a beam of penetrating radiation appearing to emanate from a common point, said beam being composed of a plurality of wave lengths each having a predetermined intensity, comprising the steps of placing a suitably shaped diffracting crystal on a focussing circle to diffract radiation to a given focus, said crystal having a plurality of reflecting planes for diffracting to said focus each of a plurality of wave lengths generated in a plurality of sources, placing each of said sources on said focussing circle, pointing each of said sources each of which emits at least one wave length which is different from that emitted from another source at the crystal from the direction of a radius drawn from the intersection of a sphere of reflection and a reciprocal lattice point, the radius of said sphere being equal to the reciprocal of said wave length, orienting said crystal to intercept radiation from each of said sources and diffract only one wave length from each source in said given common direction, and adjusting the intensity of radiation from each of said sources to thereby form a beam of radiation in which each of said wave lengths has a predetermined intensity.

7. A method of generating an intensified beam of penetrating radiation of given wave lengths comprising the steps of orienting each of a plurality of sources each 3,418,467 5 6 of which emits radiation including said Wave lengths to- OTHER REFERENCES Ward a E dlfiractmg crystal i posmomng i Fundamentals of Optics, Jenkins et al., McGraw-Hill, crystal to lntercept and difiract radiation only of said New York 1950, Pages 5 and Wave lengths from each of said sources in a common duectlon- 5 RALPH G. NILSON, Primary Examiner.

A. L. BIRCH, Assistant Examiner.

References Cited US. Cl. X.R.

UNITED STATES PATENTS 3,046,399 7/1962 Ladell 250 51.s 25 '8431356 

